The present invention relates to a regulator. In particular, the present invention relates to a regulator for regulating the pressure within a crankcase ventilation system. In particular, the present invention provides a regulator suitable for use in a pumped crankcase ventilation system. In certain embodiments of the present invention, the regulator may be used in a crankcase ventilation system further incorporating a separator for separating particulate, liquid and aerosol contaminants from a blow-by gas stream within a reciprocating engine.
Blow-by gas within a reciprocating engine is generated as a by-product of the combustion process. During combustion, some of the mixture of gases escape past piston rings or other seals and enter the engine crankcase outside of the pistons. The term “blow-by” refers to the fact that the gas has blown past the piston seals. The flow level of blow-by gas is dependent upon several factors, for example the engine displacement, the effectiveness of the piston cylinder seals and the power output of the engine. Blow-by gas typically has the following components: oil (as both a liquid and an aerosol, with aerosol droplets in the range 0.1 μm to 10 μm), soot particles, nitrous oxides (NOx), hydrocarbons (both gaseous hydrocarbons and gaseous aldehydes), carbon monoxide, carbon dioxide, oxygen, water and other gaseous air components.
If blow-by gas is retained within a crankcase with no outlet the pressure within the crankcase rises until the pressure is relieved by leakage of crankcase oil elsewhere within the engine, for example at the crankcase seals, dipstick seals or turbocharger seals. Such a leak may result in damage to the engine.
In order to prevent such damage, and excessive loss of oil, it is known to provide an outlet valve which allows the blow-by gas to be vented to the atmosphere. However, with increasing environmental awareness generally, and within the motor industry in particular, it is becoming increasingly unacceptable to allow blow-by gas, which is inevitably contaminated with oil and other contaminants from within the crankcase, to simply be vented to atmosphere. Furthermore, such venting increases the speed at which crankcase oil is consumed.
Consequently, it is known to filter the blow-by gas. The filtered blow-by gas may then either be vented to the atmosphere as before (in an open loop system), or it may be returned to an air inlet of the engine (in a closed loop system). The filtering may be performed by passing the blow-by gas through a filtering medium, or another known form of gas contaminant separator. For a closed loop system, filtration is required in order to remove oil, soot and other contaminants to protect engine components from fouling and any resultant reduction in performance or failure of a component.
The conventional arrangement of an engine blow-by gas/oil separator returning cleaned gas to an engine air intake is commonly referred to as a Closed Crankcase Ventilation system (CCV). This system requires the use of a crankcase pressure regulator in order to ensure that an excessive proportion of the vacuum generated by the engine air intake is not translated via the CCV separator to the engine crankcase.
Referring now to FIG. 1, this illustrates the arrangement of a conventional CCV system 2 coupled to a diesel engine 4. Blow-by gas from the engine crankcase passes to the CCV system 2 along inlet duct 6. The CCV system 2 comprises a regulator 8 coupled to the inlet duct 6 and a contaminant separator 10 in series. The regulator 8 and separator 10 are not visible in FIG. 1, however FIG. 2 is a flow chart schematically illustrating the arrangement of the components of the CCV system.
A pump 12 may optionally be provided within the CCV system to increase the pressure drop across the separator 10, thereby increasing the filtering efficiency. Cleaned blow-by gas exits the CCV system through gas outlet 14 and is returned to the engine air intake system. Specifically, the engine air intake system draws in air from outside of the vehicle through an inlet 16, the air then passing through an inlet air filter and silencer 18, a compressor 20 driven by a turbo charger 22 (in turn driven by the engine exhaust 24) and an after cooler 26 to cool the compressed air before it is supplied to the engine 4. The cleaned blow-by gas passes from the gas outlet 14 to the compressor 20. Oil and other contaminants separated from the blow-by gas are returned to the engine crankcase through oil drain 28.
In the system of FIGS. 1 and 2 a portion of the vacuum generated between the turbocharger 22 and the air filter 18 is lost over the blow-by separator 10. Any remaining vacuum otherwise exposed to the engine crankcase is controlled by the regulator 8. It can be seen that the total air flow drawn by the turbo compressor 22 is not necessarily restricted by the closing of the regulator, since the difference can be drawn via the engine air filter 18.
A conventional regulator 8 known for use in a CCV system is illustrated in FIG. 3. The regulator 8 comprises a floating diaphragm 30 which is arranged to open or close to restrict blow-by gas flow and pressure as required. Blow-by gas enters a first regulator chamber 32 through the CCV gas inlet 6. The diaphragm 30 at least partially occludes the gap between the first chamber 32 and a second chamber 34 (in turn coupled to the separator 10). A first side of diaphragm 30 is exposed to the blow-by gas in chamber 32. A second side of the diaphragm 30 is exposed to an ambient gas pressure within a chamber 36, which has an opening to the ambient environment. Alternatively, the third chamber may be coupled to a different pressure reference.
Movement of the diaphragm 30 is controlled by first and second springs 38, 40. Spring 38 is positioned within the second chamber and resists movement of the diaphragm 30 to close the gap between the first and second chambers 32, 34. Spring 40 is positioned within the third chamber 36 and resists movement of the diaphragm 30 to open the gap between the first and second chambers 32, 34. Adjustment of the response of springs 38, 40 and adjustment of the relative sizes of the first and second sides of the diaphragm 30 acted upon by the blow-by gas and the ambient gas pressure can be used to control the rate and extent of movement of the diaphragm 30.
The application of an integral pump 12 to improve the separation performance of a CCV system 2 is relatively new. The pressure in the first chamber 32 is regulated to the desired crankcase pressure by specification of the pump to generate the required vacuum and specifying appropriate pressure regulation spring forces. The pressure in the second chamber 34 is defined by the differential pressure loss across the separator and the vacuum generated by the integral pump 12. The vacuum generated is determined according to the operating point along the chosen pump's flow versus pressure performance curve.
It will be appreciated that for a pumped CCV separator system the flow through the pump can be entirely restricted by the position of the regulating diaphragm. For the regulator illustrated in FIG. 3, if the diaphragm 30 comes into contact with the end of tubular wall 42 separating the first and second chambers 32, 34 then gas flow between the first and second chambers is interrupted. The effect upon the pump 12 is similar to the phenomena of pump surge in which an unregulated displacement pump can give rise to spikes in the output pressure. Restricted flow resulting from a closed regulator moves the pump operating point to a corresponding low flow and high vacuum position. The increased vacuum generated in the second chamber further increases the force acting on the vacuum regulation springs 38, 40 and flow of blow-by gas is restricted yet further. Only greater force acting upon the diaphragm 30 generated by a build up of positive pressure in the engine crankcase can open the regulator again. As discussed above, excessive pressure build up in a crankcase can result in damage to the crankcase and escape of oil. A closed loop control cycle of high and low pressure hunting results between the regulator and the pump which cannot be controlled with a conventional linear response regulator.
It will be further appreciated that the problems of high and low pressure hunting for pumped CCV systems may also be experienced within other forms of crankcase ventilation systems. Specifically, pressure hunting may occur in open crankcase ventilation systems, non-pumped closed crankcase ventilation systems and exhaust pumped ventilation systems. More generally, the problems discussed above associated with conventional regulators may occur in any system which includes a pressure regulator.